Component with compressive residual stresses, process for producing and apparatus for generating compressive residual stresses

ABSTRACT

The inventive method discloses the local, adapted and controlled introduction of internal compressive stress in convex and concave regions, such as the root region of turbine blades, by means of at least two pressure generators.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2004/014300, filed Jan. 15, 2004 and claims the benefitthereof. The International Application claims the benefits of EuropeanPatent application No. 04000775.9 filed Jan. 15, 2004. All of theapplications are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention relates to a component having compressive residualstresses in accordance with the claims and to a process for producing acomponent having compressive residual stresses as described in theclaims and to an apparatus for generating compressive residual stressesas described in the claims.

BACKGROUND OF THE INVENTION

Compressive residual stresses are often introduced into components whichare subject to high mechanical loads, to enable the components towithstand increased stresses. This is in some cases carried out in thecase of fir-tree-like roots of blades or vanes of turbines (steamturbines, gas turbines).

Compressive residual stresses can be introduced by roller-burnishing.Another way of generating compressive residual stresses is shot-peening.U.S. Pat. No. 5,911,780 shows a method of this type for generatingcompressive residual stresses.

U.S. Pat. No. 5,492,447 discloses a process for generating compressiveresidual stresses in rotor components by means of a laser.

A similar process is disclosed in EP 731 184 B1.

WO 01/15866 A1 shows a process for the surface treatment of a componentin which at least one peening parameter in an abrasive peening processis adapted to the contour line of the component. DE 197 42 137 A1 showsa rolling apparatus for generating compressive residual stresses.

U.S. Pat. No. 4,428,213 discloses a component in which a first regionand then the entire component are shot-peened with a lower intensity.

EP 0 230 165 A1 and EP 1 125 695 A2 disclose a robot which guides a toolwith respect to a component that is to be processed.

U.S. Pat. No. 4,937,421 discloses a laser irradiation method and anassociated apparatus, in which the laser beam from a laser is split intotwo beams in order in this way to generate a larger irradiation surfacearea on the component to be processed, thereby achieving a fasterprocessing time. These two laser beams are guided jointly and have thesame parameters in terms of angle of incidence and intensity, and areguided jointly in one holder.

Components according to the prior art do not have sufficient strengthfor unusual operating states with regard to the desired demands imposedon the locally different operating stresses.

SUMMARY OF THE INVENTION

Therefore, it is an object of the invention to overcome this problem.

The object is achieved by the component, by the process and by theapparatus for generating compressive residual stresses in a component asclaimed in the claims.

Further advantageous measures are listed in the subclaims. The measureslisted in the subclaims can be combined with one another in advantageousways.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 show a component which has a curved surface,

FIG. 3 shows a schematic arrangement of an apparatus which can be usedto carry out the process according to the invention,

FIGS. 4, 18, 19 (schematically) show the lateral profile of thecompressive residual stresses,

FIGS. 5 to 13, 20, 21 show various process sequences of the processaccording to the invention,

FIG. 15 shows a turbine blade or vane,

FIG. 14 shows a compressive stress profile plotted over the depth of acomponent,

FIG. 16 shows a gas turbine,

FIG. 17 shows a steam turbine.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a component 1 having a surface 5. The component 1 may be acomponent of a steam turbine (FIG. 17) or of a gas turbine, such as forexample an aircraft turbine or a turbine for generating electricity 100(FIG. 16). Components of this type are, for example, turbine blades orvanes 120, 130, 342, 354, a combustion chamber lining or other housingparts.

The surface 5 of the component 1, 120, 130, 342, 354 is composed, forexample, of a plurality of, in this case two, surface regions 4, 6. Asurface region 6 (for example main blade or vane region 40, FIG. 15) is,for example, planar or has just a single curvature, whereas the surfaceregion 4 is multiply curved. Different compressive residual stressesσ_(E) that are different than zero are present in the surface 5 and itssurface regions 4 and/or 6.

The component 1, 120, 130, 342, 354 has a concavely curved region 7 ofthe surface region 4, which for example while the component 1, 120, 130,342, 354 is in use is exposed to higher mechanical stresses thananother, convexly curved region 10 of the surface region 4.

The surface region 4 of the component 1, 120, 130, 342, 354 at least inpart has concavely 7 (a valley 11) and convexly 10 curved regions (peakdome 12), resulting in local maxima 10′ and local minima 7′. A convexlycurved region 10, 12 for example adjoins the concavely curved region 7,11.

By way of example, a higher external mechanical stress is applied to theconcavely curved region 7, 11 than to the convexly curved region 10, 12when the component 1, 120, 130, 342, 354 has been installed.

Compressive residual stresses σ_(E) can be introduced in the surfaceregion 4 by surface treatment processes. This is done by means ofsuitable pressure generators 25 (FIG. 3), for example byroller-burnishing, shot-peening or laser irradiation.

As installed component 1, FIG. 2 shows, by way of example, a subregionof a turbine blade or vane 13 (FIG. 15), namely a blade or vane root 43(FIG. 15) in its securing region 16 (FIG. 15) with its fir-tree-like ordovetail-like structure as multiply curved surface region 4.

The blade or vane root 43 is, for example, arranged and held in asuitably shaped disk 22. The disk 22 is in turn arranged on a shaft 103of a gas turbine 100 (FIG. 16) or steam turbine (FIG. 17). Highmechanical loads occur in particular in the concavely curved region 7,11. Therefore, there is a need to influence the component 1 locally inthese regions in such a way that it is possible for higher tensilestresses to be withstood there, by virtue of the local tensile stressesbeing at least partially compensated for. However, this has to be donein a controlled way and as a function of the geometry in targetedfashion using locally different compressive residual stresses σ_(E).

The turbine blade or vane 13 can also be secured to the shaft 103.

FIG. 3 diagrammatically depicts how a pressure generator 25 andcomponent 1, 120, 130, 342, 354 are moved with respect to one another.According to the invention, compressive residual stresses σ_(E) aregenerated in the component 1, 120, 130, 342, 354 starting from thesurface region 4 and extending into the depth of the component 1, 120,130, 342, 354.

This can be done in particular by roller-burnishing, laser irradiationor shot-peening. By way of example, the process according to theinvention is explained in more detail on the basis of shot-peening. Thefundamental procedure and the choice of parameters can be transferredanalogously to laser irradiation, roller-burnishing or other processesused to generate compressive residual stresses. (A mechanical momentumof the shot corresponds to a power density of a laser or a contactpressure of a roller-burnishing tool.)

A shot-peening nozzle 25 as pressure generator blasts out peeningabrasive 28 (shot) at a certain velocity, forming a particle jet 29, inparticular a shot jet 29. The shot 28, in particular steel shot,impinges on the surface region 4 of the component 1 where, by virtue ofits mechanical momentum, it generates a peening pressure on the surfaceregion 4, so that compressive residual stresses σ_(E) are generatedthere.

The shot-peening nozzle 25 can be controlled using laser beams 34 from alaser 31 in such a way that it is also accurately guided along curvedcontours in the predefined region. In particular the distance, the angleof incidence α, i.e. the angle of the shot-peening nozzle 25 withrespect to the surface 5 in the surface region 4, 6, can be adapted. Theangle of incidence α is, for example, less than 90° and is in particularbetween 80° and 85°.

It is also possible for the peening pressure of the shot jet 29 to beset for the shot-peening nozzle 25. Further parameters include the sizeof the peening abrasive 28, the material of the peening abrasive 28 orthe shape of the nozzle opening (laser: beam shape; roller-burnishing:shape of the tool).

The component 1 is, for example, clamped in a fixed position, in whichcase, by way of example, in a first process step the laser beams 34 ofthe laser 31 scan the surface region 4 of the component 1 under CNCcontrol. In this arrangement, either the component 1 is mounted on a CNCmachine and displaced with respect to the laser 31, or vice versa.

The precise geometry of the component 1 is recorded by this scanning ofthe surface region 4 of the component 1. Stipulation of defined regions(for example the concavely curved regions 7) defines regions which aretreated using the shot-peening nozzle 25. It is also possible for therecording of the surface region 4 to be followed, for exampleautomatically, by a calculation which determines which regions areexposed to particularly high mechanical loads, so that the extent andlevel of the compressive residual stresses σ_(E) which are to begenerated by means of shot jets 29 can be defined accordingly.

The level of the compressive residual stresses σ_(E) which is to begenerated is also used to define the parameters of the shot-peeningnozzle 25 with respect to the concave or convex regions 7, 10 which areto be peened. This is therefore a method in which the surface region 4is treated with different parameters in a locally targeted way in aprocess, so that after the process has been carried out, locallypredefined but different compressive residual stresses σ_(E) are presentover the entire surface.

The entire surface region 4 on which compressive residual stresses σ_(E)are present corresponds, for example, to the surface of a fir-tree-likeblade or vane root 43 of the turbine blade or vane 13, 120, 130, 342,354. In this context, the term locally different means that regionswhich have high and lower compressive residual stresses σ_(E) that aredifferent than zero are generated after the process has been carriedout.

For example, high compressive residual stresses σ_(E) are generated inparticular in the concavely curved regions 7, 11, whereas lowercompressive residual stresses σ_(E) are generated in the remainingconvexly curved regions 10, 12. In particular, no curved surface 7,remains untreated, so that at least one convexly curved region 10 and aconcavely curved region 7 have compressive residual stresses σ_(E) intheir entire surface region.

The shot jet 29 is controlled by the laser 31 and, for example, by a CNCmachine which moves the shot jet 29 with respect to the component 1 inorder to allow different regions 7, 10 to be peened.

FIG. 4 a) shows an exemplary distribution of the compressive residualstresses σ_(E) in an x-y plane.

In the concavely curved region 7, 11, which has the higher compressiveresidual stresses σ_(E), there is a maximum 70 in the compressiveresidual stress σ_(E) within the x-y plane. The convexly curved region10, 12 has a plateau 74 of lower compressive residual stresses σ_(E).However, the maximum 70 and all the values for the region 7, 11 arehigher than the value of the plateau 74.

Therefore, the term locally different compressive residual stressesmeans that the compressive residual stresses σ_(E) are higher in theconcavely curved region 7, 11 than in the plateau 74 in the convexlycurved region 10, 12 having the lower compressive residual stressesσ_(E).

FIG. 4 b) shows a further exemplary distribution of the compressiveresidual stresses σ_(E) in an x-y plane.

In the concavely curved region 7, 11, which has the higher compressiveresidual stresses σ_(E), there is a maximum 70 in the compressiveresidual stress σ_(E) within the x-y plane. The convexly curved region10, 12 has a maximum 73 of lower compressive residual stresses σ_(E).

However, the maximum 70 is higher than the maximum 73. Therefore, theterm locally different compressive residual stresses means that themaximum 70 in the compressive residual stress σ_(E) in the region 7, 11is higher than the maximum 73 in the convexly curved region 10, 12having the lower compressive residual stresses σ_(E).

Although the concavely curved region 7, 11, as can also be seen in FIG.4 b), at some locations has lower compressive residual stresses σ_(E)than the convexly curved region 10, 12, in particular in the transitionregion between the concavely curved region 7, 10, this means that it isnot a punctiform comparison of compressive residual stresses σ_(E) thatshould be used to define the regions with higher compressive residualstresses σ_(E) and lower compressive residual stresses σ_(E), but ratherthe height of the maxima 70, 73 should be used as the basis for suchcomparison.

FIG. 18 shows a component 1 according to the invention.

The concavely curved region 7 has a minimum 7′ which has a definedradius of curvature R. The radius of curvature R is determined at thepoint of the minimum 7′ in a known way. A width 81 of the concavelycurved region 7, 11, in which the higher compressive residual stressesσ_(E) are present, is at least 3-5 times the radius of curvature R andis in particular arranged centrally around the minimum 7′. The concavelycurved region 7, 11 having the width 81 is adjoined, in the direction ofthe longitudinal axis 37, by at least one convexly curved region 10, 12having the lower compressive residual stresses σ_(E).

The compressive residual stress σ_(E) in the concavely curved region 7,11 having the higher compressive residual stresses σ_(E) is at least 30%or 50% or 60%, in particular 75%, higher than the compressive residualstresses σ_(E) in the convexly curved region 10 having a lowercompressive residual stress σ_(E).

The level of the compressive residual stresses σ_(E) in the concavelycurved region 7 can also be correlated with a yield strength R_(p) ofthe material of the component 1, 120, 130, 342, 354.

By way of example, it is possible to use the yield strength R_(p 0.2),in which case, for example, the compressive residual stress σ_(E) is atleast 30%, in particular at least 50% of the yield strength R_(p 0.2).

The component 1 or the blade or vane root 43 of the turbine blade orvane 13, 120, 130, 342, 354 extends in a direction 17, for example fromone end 91 to the other end 94 (FIG. 19) perpendicular to thelongitudinal axis 37. The concavely curved region 7, 11 is a curvedsurface having a width 3 to 5 times R (=81) about a line 85 whichconnects the minima 7′ to one another in direction 17. In direction 17,the concavely curved region 7, 11 extends over the width of thecomponent 1, 120, 130, i.e. from the end 91 to the end 94. The width 81is the length of the curved contour profile about the minimum 7′.

If, in accordance with the prior art, only a single shot-peening nozzle25 is used, first of all it is only possible to generate highcompressive residual stresses σ_(E), and it is not then possible togenerate low compressive residual stresses σ_(E), or vice versa.

FIG. 5 shows a subregion of the surface 5 of a component 1, 13, 120,130, 342, 354.

In a first process step, shot-peening of a concavely curved region 46 iscarried out with a high peening pressure.

In a further process step, other, adjacent regions 49 are treated, usingshot-peening with a lower peening pressure (FIG. 6).

The process can be applied to newly produced components 1, 120, 130,342, 354 and to refurbished components 1, 120, 130, 342, 354.

Refurbishment means that after they have been used components 1 ifappropriate have layers removed from them or are examined for cracks,which are repaired if appropriate. Compressive residual stresses σ_(E)are then generated again.

FIG. 7 shows an apparatus in accordance with the prior art which can beused to carry out the process.

In this apparatus, only a single shot-peening nozzle 25 is used.

In a first step, a high peening pressure is introduced in the region 46(concavely curved region).

Then, a shot jet 29 is diverted onto the regions 49 (concavely curvedregion) in which lower peening pressures are to be generated, by moving(cf. arrow) the shot-peening nozzle 25 or the component 1, for exampleby varying the angle of incidence.

This can be achieved by the shot 28 used in the region 46 being subjectto lower velocities and therefore lower mechanical momentums or by theshot-peening nozzle 25 blasting out shot 28 of smaller diameter 58 intothe regions 49.

If the shot 28 has a smaller diameter, it is possible to generatedifferent peening pressures, for example by the materials of the shothaving different hardnesses. By way of example, ceramic material can beused for hard material and metallic material can be used as softmaterial.

Large shot 55 generates a higher peening pressure than smaller shot 58given the same velocity.

It is also possible to use small ceramic shot and large metallic shot.

Further possible combinations of different materials, diameters andshape of the shot are conceivable, for example in order to achieve anabrasive action or to reduce the roughness or to achieve a smoothingaction.

If, in accordance with the invention, a plurality of shot-peeningnozzles 25, 25′, 25″, 25′″, 25″″ are used, these nozzles can be operated

a) individually or in pairs at successive time intervals or

b) simultaneously.

If the shot-peening nozzles 25, 25′, 25″, 25′″, 25″″ are operatedsimultaneously, the shot-peening nozzles 25, 25′, 25″, 25′″, 25″″ may bearranged locally at the same height (FIG. 9) or may be offset withrespect to one another, i.e. one or more shot-peening nozzles are in aleading position and the other or others are in a trailing position(FIGS. 10, 11).

FIG. 8 shows an apparatus 2 which can be used to carry out the processaccording to the invention.

In this apparatus 2, by way of example, a plurality of, at least two, inthis case three shot-peening nozzles 25, 25′, 25″ are used.

By way of example, the shot-peening nozzle 25 can be used first of all,in order to expose the region 46 (concavely curved region) to a highpeening pressure.

In a second step, only the other shot-peening nozzles 25′, 25″ are used,in order to expose the regions 49 (concavely curved region) to lowerpeening pressures (for example for smoothing purposes).

It is also possible for the three shot-peening nozzles 25, 25′, 25″shown by way of example in FIG. 8 to be operated simultaneously (togenerate compressive residual stresses and to provide a smoothingaction).

In this case, one or two shot-peening nozzles 25′, 25″, for examplewhich generate lower peening pressures, can likewise effect peening intothe region 46 (i.e. peening a region 52, FIG. 6) (FIGS. 10, 11).

In this case, a shot-peening nozzle 25 generates a high peening pressureand peens the concavely curved region 46, and the second or furthershot-peening nozzle 25′, 25″ generates a lower peening pressure than theshot-peening nozzle 25 and peen at least the convexly curved region 49.

It is also possible for the shot-peening nozzle 25 to have shot 28 of asmaller diameter 58 in order to generate high intensities and highcompressive residual stresses, and for the shot-peening nozzles 25′, 25″to carry out peening using shot 28 of a larger diameter 55, generatinglow intensities and lower compressive residual stresses in the regions49, while at the same time peening into the region 46 in order to smooththe latter (FIG. 20).

The choice of parameters can be adapted to the specific demands imposedon the level of compressive residual stresses and smoothing.

It is also possible for a single shot-peening nozzle 25 to have shot ofdifferent diameters 55, 58 and to simultaneously peen a defined region,in this case the regions 46, 49 (FIG. 21).

Irrespective of whether the shot-peening nozzles 25, 25′, 25″ areoperated simultaneously or in succession at time intervals, differentparameters can be set for each shot-peening nozzle 25, 25′, 25″.

The peening pressure, the size of the peening abrasive 28, the materialof the peening abrasive 28 or the angle of incidence α can be selectedas parameters for the shot-peening nozzle 25, 25′, 25″.

In particular, the shot-peening nozzle 25 and the shot-peening nozzles25′, 25″ have different parameters, in particular different peeningpressures. The shot-peening nozzles 25, 25′, 25″ may be present at onelevel next to one another, i.e. as indicated in FIG. 9, or may bearranged behind one another (FIGS. 10, 11).

The different parameters for the shot-peening nozzles 25, 25′, 25″ arepredetermined and the regions 46, 49 are moved over for example in oneoperation. This takes place, for example, in such a way that theshot-peening nozzles 25, 25′, 25″ are, for example, in a fixed positionand the component 1 is mounted on a movable base (CNC machine) and ismoved beneath the shot-peening nozzles 25, 25′, 25″. The component 1 canalso be moved in reciprocating fashion, so that the regions 46, 49 arepeened more than once. This procedure means that the regions 7, 10 inwhich different compressive residual stresses are to be generated do nothave to be successively exposed to shot jets. This leads to aconsiderable time saving.

The region on the surface 5 of the component 1 which is peened by ashot-peening nozzles 25, 25′, 25′ may be round or oval, with theindividual regions adjoining one another.

FIG. 9 shows a plan view onto the regions 46 and 49 and the exemplaryarrangement of shot-peening nozzles 25, 25′ and 25″ used. Theshot-peening nozzles 25, 25′, 25″ are in this case arranged at the samelevel.

The shot-peening nozzles 25, 25′, 25″ are moved over the regions 46 and49 in a direction of movement 26. This can take place in one workingstep, in which all three nozzles 25, 25′ and 25″ are operatedsimultaneously, in which case a higher compressive residual stress σ_(E)is generated in the region 46 by the shot-peening nozzle 25 and lowercompressive residual stresses σ_(E) are generated in the adjoiningregions 49.

The shot-peening nozzle 25 and the shot-peening nozzles 25′ and 25″ canalso be operated in succession at time intervals. For example, in afirst process step it is possible for only the shot-peening nozzle 25 tobe operated, which then generates high compressive residual stressesσ_(E) in the region 46. In a second or further process steps, theshot-peening nozzle 25 is no longer operated, but instead theshot-peening nozzles 25′ and 25″ are operated, which generate lowercompressive residual stresses σ_(E) in the regions 49 adjoining theregion 46. The nozzles 25′, 25″ may also be offset with respect to thenozzle (FIG. 11).

In this case, the shot-peening nozzles are, for example, jointly mountedon a carrier and are moved jointly even when they 25, 25′, 25″ are notoperating, i.e. shot-peening, together.

FIG. 10 shows a further way of generating compressive residual stressesσ_(E) in the regions 46 and 49.

The openings of the shot-peening nozzles 25′ and 25″ are in this case,for example, elongate in form or produce an elongate impingement surfaceon the component 1, 120, 130, 342, 354 and cover, for example, both theregion 49 and the adjoining region 46. This is desirable, for example,if the region 46 is to be smoothed in this way. Therefore, theshot-peening nozzles 25′ and 25″ are locally offset with respect to theshot-peening nozzle 25 in the direction of movement. By way of example,the shot-peening nozzle 25 is arranged in a leading position and theshot-peening nozzles 25′ and 25″ in a trailing position. In this casetoo, the shot-peening nozzles 25, 25′ and 25″ can be operated at thesame time or in succession.

By way of example, the nozzle 25 can be used to generate compressiveresidual stresses σ_(E) and the nozzles 25′, 25″ can be used forsmoothing purposes.

In this case, the shot-peening nozzles are, for example, mounted jointlyon one carrier and are moved together, even when they 25, 25′, 25″ arenot operating, i.e. shot-peening, together.

FIG. 11 shows a further arrangement of shot-peening nozzles. In thiscase, five shot-peening nozzles 25, 25′, 25″, 25′″ and 25″″ are used.The parameters for the individual shot-peening nozzles 25 and 25′, 25″and 25′″ and 25″″ can in each case be different and adapted to thedesired requirements.

By way of example, the nozzles 25, 25′, 25″ can be used to generatecompressive residual stresses σ_(E) and by way of example the nozzles25′″, 25″″ can be used to provide a smoothing action.

The shot-peening nozzle 25 covers the region 46, whereas theshot-peening nozzles 25′, 25″ cover in each case only the respectivelyadjoining regions 49.

The shot-peening nozzles 25′″, 25″″ which follow in local terms are usedto provide a smoothing action and in this case, by way of example, coverboth the region 46 and the region 49.

In this case, the shot-peening nozzles are, for example, mounted jointlyon a carrier and are moved jointly, even when they 25, 25′, 25″ are notoperating, i.e. shot-peening, together.

FIG. 12 shows, as component 1, a turbine blade or vane 13 including itsblade or vane root 43, which is of fir-tree-like design in the securingregion 16. The blade or vane root 43 has concavely curved regions 7, inwhich high compressive residual stresses σ_(E) are to be present, andhas convexly curved regions 10, in which lower compressive residualstresses σ_(E) than in the convexly curved region 7 are to be present.

The blade or vane root 43 has, for example, three valleys or grooves11′, 11″, 11′″, the three shot-peening nozzles 25, 25′, 25″, for examplein terms of their parameters, being set fixedly with respect to thefirst groove 11′.

The turbine blade or vane 13 or the component 1 is displaced along adirection 17 with respect to the shot-peening nozzles 25, 25′ and 25″,so that the entire groove 11′ is peened. This operation can be repeatedfor the further grooves 11″ and 11′″, or further shot-peening nozzlesare correspondingly present for the grooves 11″ and 11′″, allowingsimultaneous processing of all the grooves.

FIG. 13 diagrammatically indicates that the edges of the grooves 11′,11″, 11′″ are likewise peened in order to generate compressive residualstresses σ_(E). It can also be seen that the component 1 is inherentlycurved.

FIG. 14 shows the theoretical profile of the compressive residual stressσ_(E) in a component 1 as results from a peening operation.

The diagram plots the compressive residual stress σ_(E) over the depth dof a component 1. The maximum 67 of the compressive residual stressσ_(E) does not lie at the surface 4 of the component 1, i.e. at d=0, butrather in the interior of the component 1 (d>0). The curve 61illustrated by a dashed line shows the profile of the compressiveresidual stress σ_(E).

However, it is desirable for a maximum value of the compressive residualstress σ_(E) to be present at the surface 5 of the component 1. Thesolid line of curve 64 shows this desired profile of the compressiveresidual stress σ_(E).

The desired profile 64 can be achieved, for example, in the followingway. In a first operation, a concavely curved region 7, 10 is peenedusing a high peening pressure. In a second operation, the same region 7,10 is peened with a lower intensity, so that the maximum shifts to thesurface 5 of the component 1. However, this may also take place in asingle operation as described above.

The result of this is that the maximum of the compressive residualstress σ_(E) is present at the surface 5 or near to the surface 5 yetnevertheless there is a high depth of penetration of the compressiveresidual stress σ_(E) into the component 1.

FIG. 15 shows a component 13 which can be treated by means of theprocess according to the invention.

FIG. 15 shows a perspective view of a turbine blade or vane 13 forexample for a steam turbine, which extends along a longitudinal axis 37.In the case of conventional turbine blades or vanes 13, solid metallicmaterials are used in all regions 40, 19, 43 of the rotor blade 1.

The turbine blade or vane 13 can in this case be produced by a castingprocess, by a forging process, by a milling process or by combinationsthereof. The turbine blade or vane 13 has, in succession along thelongitudinal axis, a securing region 16, an adjoining blade or vaneplatform 19 and a main blade or vane region 40. A blade or vane root 43,which is used to secure the turbine blade or vane 13 to the disk 22 of aturbomachine (not illustrated), is formed in the securing region 16. Theblade or vane root 43 is configured in the shape of a hammerhead. Otherconfigurations, for example as a fir-tree root (FIG. 2) or a dovetailroot, are possible.

The fir-tree root 43 has compressive residual stresses that aredifferent than zero at least in a concavely curved region 7 and theadjoining convexly curved region 10, so that compressive residualstresses are present over a large area at the surface of the blade orvane root, in particular everywhere.

FIG. 16 shows, by way of example, a partial longitudinal section througha gas turbine 100.

In the interior, the gas turbine 100 has a rotor 103 which is mountedsuch that it can rotate about an axis of rotation 102 and is alsoreferred to as the turbine rotor. An intake housing 104, a compressor105, a, for example, toroidal combustion chamber 110, in particular anannular combustion chamber 106, with a plurality of coaxially arrangedburners 107, a turbine 108 and the exhaust-gas housing 109 follow oneanother along the rotor 103.

The annular combustion chamber 106 is in communication with a, forexample, annular hot-gas passage 111, where, by way of example, foursuccessive turbine stages 112 form the turbine 108.

Each turbine stage 112 is formed from two blade or vane rings. As seenin the direction of flow of a working medium 113, in the hot-gas passage111 a row of guide vanes 115 is followed by a row 125 formed from rotorblades 120.

The guide vanes 130 are secured to the stator 143, whereas the rotorblades 120 of a row 125 are fitted to the rotor 103 for example by meansof a turbine disk 133. A generator (not shown) is coupled to the rotor103.

While the gas turbine 100 is operating, the compressor 105 sucks in air135 through the intake housing 104 and compresses it. The compressed airprovided at the turbine-side end of the compressor 105 is passed to theburners 107, where it is mixed with a fuel. The mix is then burnt in thecombustion chamber 110, forming the working medium 113. From there, theworking medium 113 flows along the hot-gas passage 111 past the guidevanes 130 and the rotor blades 120. The working medium 113 is expandedat the rotor blades 120, transferring its momentum, so that the rotorblades 120 drive the rotor 103 and the latter in turn drives thegenerator coupled to it.

While the gas turbine 100 is operating, the components which are exposedto the hot working medium 113 are subject to thermal stresses. The guidevanes 130 and the rotor blades 120 of the first turbine stage 112, asseen in the direction of flow of the working medium 113, together withthe heat shield bricks which line the annular combustion chamber 106,are subject to the highest thermal stresses. To be able to withstand thetemperatures which prevail there, they are cooled by means of a coolant.

The substrates may likewise have a directional structure, i.e. they arein single-crystal form (SX structure) or have only longitudinallyoriented grains (DS structure). Iron-base, nickel-base or cobalt-basesuperalloys are used as material.

The blades or vanes 120, 130 may also have coatings which protectagainst corrosion (MCrAlX; M is at least one element selected from thegroup consisting of iron (Fe), cobalt (Co), nickel (Ni), X stands foryttrium (Y) and/or at least one rare earth element) and heat by means ofa thermal barrier coating. The thermal barrier coating consists, forexample, of ZrO₂, Y₂O₄—ZrO₂, i.e. unstabilized, partially stabilized orfully stabilized by yttrium oxide and/or calcium oxide and/or magnesiumoxide.

Columnar grains are produced in the thermal barrier coating by suitablecoating processes, such as for example electron beam physical vapordeposition (EB-PVD).

The guide vane 130 has a guide vane root (not shown here) which facesthe inner housing 138 of the turbine 108, and a guide vane head which isat the opposite end from the guide vane root. The guide vane head facesthe rotor 103 and is fixed to a securing ring 140 of the stator 143.

FIG. 17 illustrates, by way of example, a steam turbine 300, 303 with aturbine shaft 309 extended along an axis of rotation 306.

The steam turbine has a high-pressure part-turbine 300 and anintermediate-pressure part-turbine 303, each with an inner casing 312and an outer casing 315 surrounding it. The high-pressure part-turbine300 is, for example, of pot-type design. The intermediate-pressurepart-turbine 303 is of two-flow design. It is also possible for theintermediate-pressure part-turbine 303 to be of single-flow design.

Along the axis of rotation 306, a bearing 318 is arranged between thehigh-pressure part-turbine 300 and the intermediate-pressurepart-turbine 303, the turbine shaft 309 having a bearing region 321 inthe bearing 318. The turbine shaft 309 is mounted on a further bearing324 next to the high-pressure part-turbine 300. In the region of thisbearing 324, the high-pressure part-turbine 300 has a shaft seal 345.The turbine shaft 309 is sealed with respect to the outer casing 315 ofthe intermediate-pressure part-turbine 303 by two further shaft seals345. Between a high-pressure steam inflow region 348 and a steam outletregion 351, the turbine shaft 309 in the high-pressure part-turbine 300has the high-pressure rotor blading 354, 357. This high-pressure rotorblading 354, 357, together with the associated rotor blades (not shownin more detail), constitutes a first blading region 360. Theintermediate-pressure part-turbine 303 has a central steam inflow region333. Assigned to the steam inflow region 333, the turbine shaft 309 hasa radially symmetrical shaft shield 363, a cover plate, on the one handfor dividing the flow of steam between the two flows of theintermediate-pressure part-turbine 303 and also for preventing directcontact between the hot steam and the turbine shaft 309. In theintermediate-pressure part-turbine 303, the turbine shaft 309 has asecond blading region 366 comprising the intermediate-pressure rotorblades 354, 342. The hot steam flowing through the second blading region366 flows out of the intermediate-pressure part-turbine 303 from anoutflow connection piece 369 to a low-pressure part-turbine (not shown)which is connected downstream in terms of flow.

The turbine shaft 309 is composed, for example, of two turbinepart-shafts 309 a and 309 b, which are fixedly connected to one anotherin the region of the bearing 318.

1. A process for producing a turbine component, comprising: shot peeninga surface region of the component to produce a locally differentcompressive residual stress on the region by a first shot peeningnozzle; and shot peening the surface region to produce a smoothedsurface finish by a second shot peening nozzle, wherein the two shotpeening nozzles are operated simultaneously and different peeningpressures and shot diameters are used for the two shot-peening nozzles.2. The process as claimed in claim 1, wherein the surface region has aplurality of concavely curved and a convexly curved regions.
 3. Theprocess as claimed in claim 1, wherein the second shot-peening nozzle isoperated after the first shot-peening nozzle.
 4. The process as claimedin claim 2, wherein operating parameters for the shot-peening nozzle areselected from the group consisting of: peening pressure, peeningabrasive size, peening abrasive material, peening angle of incidence,and peening blasting shape.
 5. The process as claimed in claim 2,wherein different parameters are set for the first and second nozzlesand the concavely curved regions and a convexly curved regions arepeened at the same time by multiple passes by the nozzles over theconcavely and convexly curved regions.
 6. The process as claimed inclaims 1, wherein the shot peen nozzles or the component are guided in acontrolled way based on scanning of the component regions by a laser. 7.The process as claimed in claim 6, wherein the second nozzle is operatedusing a lower peening pressure and a larger diameter shot than was usedwith the first nozzle.
 8. The process as claimed in claim 7, wherein thefirst nozzle contains shot of different size diameter.
 9. The process asclaimed in claim 8, wherein the first and second nozzles contain shot ofdifferent material hardness.
 10. The process as claimed in claim 9,wherein the shot is made from ceramic or metal.
 11. The process asclaimed in claim 10, wherein the component is a blade, a vane or a heatshield element.
 12. The process as claimed in claim 11, wherein theangle of incidence between a peening direction of a shot-peening nozzleand a curved surface of the component is between 80° and 85°.
 13. Theprocess as claimed in claim 2, wherein in a first process step ashot-peening treatment of a region is performed using a defined peeningpressure, and in a second process step the same region is peened using alower peening pressure to shift the maximum of the compressive residualstress to the surface of the component.